Process for manufacturing acid phosphate



De. 22, 1931. B. OBER ETAL.

PRocEss FOR MANUFATURING ACID PHOSBHATE 2 Sheets-Sheet l Filed March 3, 1927 Enfer-V056@ De'c. 22, 1931. f

Filed March 3, 1927 2 Sheets-Sheet 2 Painted Dele. 2z, 1931 UNITED STATES PATENT; ol-Fics ,BEYERLYVOBIR AND EDWARD HYATT WIGHT, F BALTIMORE, MARYLAND, ASSIGNORS, :BY MESN E ASSIGNMENTS, TO THE OBERPHOS COMPANY, 0F BALTIMORE, MARY- LAND, A' CORPORATION OF MARYLAND Application med March 3,

This invention relates to a process and apparatus for manufacturing acid phosphate. Y

In producing acid phosphate prior to this 5' time, predetermined amounts of phosphate rock dust and sulphuric acid have been mixed in a container of capacity varying from one to two and one half tons. This container, or mixing chamber, was provided 1'0 with an agitator or stirring mechanism usually of the rotary plow type. After a short mixing period thev resulting mass was dumped in a large den,each den taking upwards to fifty charges from the container. The acid phosphate was allowed to remain in this den for approximately twenty-four hours after which it was removed-to the curing shed. The mass resulting from the mixture of acid rock was admitted 4into the den as a heavy sludge. In the den it solidies in a spongy porous mass. This mass is quite moist and as a result difficult to handle. To accelerate the drying of this mass various expedients have been tried. Ascommon practice was to dust the mass with phosphate rock dust and other dryers. Another/ method is to frequently turn product over to allow aeration and thus facilitate evaporation of the watercontent. After the phosphate was cured it was yground or` remilled before being packed. Such processes Whichinvolved re-handling of the product demanded considerable expenditure of time `and labor, 'and .by reason of the long curing period necessitated large plant investments for dens, curing sheds and the like. L

It is the primary object of our invention to devise amethod for manufacturing acid .40 phosphate which can be effected in a much shorter ltime than could be'done heretofore. Another object Ais to provide a simple apparatus in which the several stages of 'acid phosphate manufacturemay be carried out.

`A further object istodevise an apparatus of this character which obviates the use of way valve 5.

large dens 'and curing equipment. v

Yet anothenobjectlis to devise a process, i the separatesteps of which may be carried out ina single container.

. refer to similar p PROCESS FOR MAN UFAGTURING ACID (PHOSPHATE 1927. Serial 170.172,359.

With these and other 4equally important objects in view, the invention comprehends the treatment of phosphatic material with an acid under regulated conditions of temperature and pressure in an'improved a paratus and to effectively carry out therein the several stages of acid phosphate manufacture.

To enable an easy comprehension of the invention there is shown in the accompanying drawings a preferred in which the process may these drawings t e be carried out. In same reference numerals views, of which: e

Figure 1 is an elevation of an acid phosphate unit;

type of apparatus rts throughout the severaly Fig. 2 is a plan view of the apparatus shown in 1; Fig. 3 is an end elevation of the device.

In Fgur'e 1 there is shown a complete unit adapte to produce acid phosphate according to this invention. LThis comprises a dust hopper 1 mounted on a floor 2 .or any other similar support. This hopper may be made ofv any suitable material such as heavy sheet steel. It is to be understood that this is a weighing hopper and may be provided with a small scale beam pivoted to the hopper at one end and intermediatelyto support brackets, or it may be of the two point suspension type connected to the scale through triple compound levers. For convenience a small hopper is shown but it will be understood that any preferred type of weighing hopper may be employed. -It .will be understood Vfurther that the phosphate,l dust maybe discharged from the hopper under `gravity feed orit may be forced therefrom lined with an acid resistant material such 'as regulus alloy. Leading from the tank 3 is an acid line 4 in whichis interposed a straight Positioned below the hopper and acid tank, 'is the manufacturing unit. This includes a horizontal rotary autoclave 6 which is in fluid by any other l, means. Mounted above vthe'iioor line 2 adjacent thel hopper is an acid tank 3. This may .be of'` any desired structure and should be connection with a neutralizer 7 a condenser 8 and a vacuum pump 9.

The autoclave is formed with interior and exterior shells to present an intermediate jacket for the reception of heating or cooling media in a'manner to be more particularly described. The autoclave is provided with hollow shaft extensions or trunnions 10 which are journaled in the collars 11 of supporting yA forms 12. It will be understood that the more quickly brought into loading position beneath the hopper. The interior and' exteror shells ofthe autoclave are adapted to receive a blow loff vent valve 16. On the interior of the container a suitable screen is positioned over the intake of the valve 16 to prevent clogging of the vent port. A valve 17 is mounted on a conoidal end of the autoclave and cnonnects with the jacket to serve as an air break. l

Set in the-outer cylindrical shell and opening into the jacket is a drain valve 18 adapted to withdraw fluid therefromin a manner to be more articularly described. The exterior hollow s aft 10, which is in fluid connection withv the jacket ofc-the autoclave, encloses a second 'and smaller hollow shaft 19 which connects with the interior of the container at each end of the latter. The ends of the hollow pipes 19 connect with anacid pipe 4 and a fluid draw-off linev 20. IThe shafts 10 and 19 are received in a cylindrical collar 21 suitably supported by brackets 22 on a threaded extension 23 of the A form. The collar 21 is provided with terminal flanges 24. The exterior flange is apertured to receive draw bolts adapted tomaintain a fluid tight connection between the pipes 4 andl20and the rotating shaft 19.

1t will be understood that the shaftr 1l) is suitably gasketed so as vto insure a fluid tight seal with the collar 21. The collar 21,posi tioned adjacent the acid line 4, is tapped at 25? to receive a condensed water outlet pipe. S 1milar1y,the collar 21 adjacent the draw-ofi llne 20, is apertured at 26. to receive a fluid inlet pipe so that a fluid circuit maybe setup 1n these elements and the jacket'of the autoclave, for the purposes of heatingl and coolmg the latter.

Secured to any convenient portion of the autoclave and communicating with t-he interlor are the thermometer 27 and pressure gauge 28. These may be of any standard type and are .adapted to registerthe temperature and pressure conditions within the container. At 29 there is shown diagrammatically a test draw off. This may be fitted with a one way valve. When it is desired to test the material within the autoclave at any stage in the operation the valve may be opened .and a'small quantity withdrawn.- The rotation of the autoclave may be momentarily arrested for this purpose.

'As indicated previously, the autoclave is connected to theneutralizer 7. The fluid line 20 has interposed therein a valve 30 adapted to open and close connection between the neutralizer and the autoclave. The pipe 20'is fitted with an elbow to the other end ot which is secured a short pipe section 31 which terminates adjacent the bottom of the neutralizing tank.. The tank is fitted with a gauge glass 32 to show the height of the neutralizing liquid in tank 7. Connected to the upper portion of the tank is a liquid feed line 33 through which fresh neutralizing stock is introduced.

-The flow of liquid through lthis intake line may be` controlled by suitable valves (not shown). To the bottom of the tank there is connected a draw-ofi line 34 controlled by cocks 35 and 36. Leading from the top of the neutralizing tank is a vapor draw-off line 37 which, at its other end, is directly connected to the upper part of the condenser column 8. i

The vapor line 37 is in fluid connection with the suction line 38-39. As shown, particularly in Fig. 2, the suction line 39 leads to the vacuum pump 9. Interposed in the line 39- isa regulating valve 40 and a lubricating port 41. The fluid drawn inthrough the line 39 is ejected from the pump throughthe dischargline 42.

' The vacuum pump 9, which may be of any desired construction, is provided with a driving pulley 43 which. on being rotated by any driving means, is adapted to impart reciprocatingmotion to the pump piston, to draw fluid in through the line 39 and discharge it through the line 42.

Tapped in the lower end ofthe condensing column is a cold water inlet 44. The cooling medium, such for instance as cold water, flows in continuously through this line and is withdrawn from the upper end of the column through the line 45. It is to be noted that the vapors flow down through the condenser `countercurrent to the upward flow of the cooling medium. The condensate formed in the column is' withdrawn from the bottom through the draw-off line 46 (Figz) while incondensable gases are drawn through the suction line 39. Positioned in the lower portion of the condenser,` are the sight glasses 47 through which the quantity of condensate being withdrawn may be observed.

As intimated hereinbefore, the autoclave is adapted to be rotated during the treatment of the rock. This is accomplished by j means may be employed.

l ceived from y understood that the connecting the autoclave to a driving mechanism. As shown,lparticularly in Fig.-1, this comprises a driving shaft 48 suitably connected-near one end t rough the .pulley 49 to a source ofpower and adjacent the other to transmission gearing and the autoclave. This shaft is journaled adjacent its ends in bearings carried by the support brackets 50. These brackets are fixed to the foundation blocks 13 in any desired manner; The driving pulley 49 iskeyed to the shaft and is adapted to receive motion from the motor through the intermediacy of a belt or the like.

At the other end of the shaft, adjacent the y bracket, there is keyed or otherwise fixed,` a driving gear 51. This gear meshes with driven gear 52 which is fixed vto the shaft 10 I of the autoclave. It will be understood that -whilethere is shown a simple driving mechanism any other type of motion transmission The operation of the device will lbe perthe foregoing description. Phosphate rock, ound in a Crusher to any f suitable degree o fineness, is admitted tothe hopper and weighed therein. The manhole cover 15 is removed and this measured amount of dust allowed to feed by gravity into the subjacent autoclave. As has been explained previously, the dust may be forced in under pressure. The cover is then replacedf and tightly bolted to' insure a hermetic sealing. The motor is then started and the autoclave rotated., Valve 5 is now open and a predetermined amount of acid, such as sulphuric acid, is admitted under gravity or pumpl pressure. By pouring in the acid under pressure and concomitantly rotating the autoclave, an'intimate initial mixture of the reactive` ingredients is insured. It is to be acid line may project finto the autoclave and be bent to extend 'narvodset so that it will be clear allel with, the cylindrical portion of the latter. rlhe lower portion of the acid pipe is perforated so that' the acid is, `in edect, sprayed down upon the rock. Any other suitable spraying mechanism may be employed. As the acid line enters the autoclave it is slightly of thespace beneath the manhole when the autoclave is in loading position. The amount of acid may be slightly -in excess of the theoretical quantity necessary to react with all of the dust. It is to be noted that a suilicient amount of water should 'be present to insure proper crystallization of the acid phosphate.

During the reaction period theautoclave is rotated continuously. As the acid reacts with the rock a considerable quantity of heat is generated and gaseous reaction products are evolved. By retaining the reacting mass in an air tight container relative'percentages y ofthe reacting components are maintained o elevated 'In carrying out thel process p 'this process on the .fers radically from the conventional'process of mixing in a pan wherein the mass sets up or becomes hard in a very short time. Hence the desirable asliquid medium could not be obtained. By

maintained iny the Aliquid or semi-liquid state untilv all of the` rock has become mixed.

The `digestionof the rock in the rotating line distribution of the rock in other hand, the mass is Vso container is continued until the reaction lis complete. The time required for vthis will of course vary depending on such factors as the imposed pressures, the intimacyof the mix, the temperature of reaction and so forth. The transition from the mixin verting stage may be accomplished by iii-.

creasing the temperature or decreasing the to the 'conpressure, or by a combination of both factors.

Under ordinary conditionsfrom twenty minutes to an hour is a suilicient period to allow al complete conversion f the phosphatic material. l f

After the rockl and acid have reacted -icompletely the valve 16 is opened'and'the generated gaseous products'are allowed ,to escape. If desired, at this stopped and the valve 16 coupled to a receiving tank containing an absorbing medium for the gases. After the gases have been evacu- 'ated and Vthe pressure in the autoclave reduced to atmospheric pressure, the valve 16 is closed. The vacuum pump 9 is then set in operation and the valves 40 and 30 are' opened. 'Upon operation of the pump a suction is set up in the lines 39 and 37 and the residual gases are withdrawn from the autoclave. These gases course through the pipes 20 and 3.1 and percolate through the lime or equivalent neutralizing solution in tank 7. During the passage through the neutralizing solution, most of these gases are absorbed in the solution and some substances, 'such for instance as calcium sulphate, areprecipitated out. lf desired, the liquid in the tank 7 may he continuously7 withdrawn throu h the pipe 34 while fresh stockis admitted through the i e'll. p'from the neutralizing tank the residual gaseousstream is sucked through the line 37 and downwardly through 4the condenser point thel autoclave maybe A countercurrent -to the stream of cooling mev vapor in the autoclave may be withdrawn through the pipes 20 and 28 to iow through the neutralizing tank and-condenser in the manner stated. It will be observed that during the process the reacting mass is subjected to an autogenous' pressure.- This pressure is built up by the evolution of the gas products of reaction, such for instance as carbon dioxide and hydrogen fluoride. In some cases, particularly when the raw material has a very high carbonate content, the pressure increases to such a degree as to retard the reaction beyond the desired point. When such an excessive pressure is registered on the pressure gauge it may be reduced by slightly releasing the valve 16. It is to be noted that this operation may be rendered automatic by placing an automatic release valve,-set to any desired pressure, on the autoclave. Throughout this operation the temperature obtaining in the autoclave will register on the therniometer.

7While the reaction between the rock and acid generates considerable heat we have found that the action could be further accellcrated by applying external heat. The process in which this external heat is utilized is similar to that previously described.- After the comminuted rock has been admitted 4to the L autoclave the cover' is bolted in sealed position. The valve 17 is then opened slightly and a heating medium, such as steam, admitted tothe hollow shell through the line 26. The incoming steam forces air out throughthe valve 17 which may be closed when the lspace between the interior and exterior shells is filled with steam. The superheated steam then circulates through the autoclave and out through the discharge line 25. The temperature may be controlled by regulating` the flow of the heating medium through suitable valves placed in the steam /t inlet line.

As explained in our pending application,

I' Ser. No. 112,67 8, filed, May 29, 1926, we lfind that that the reactions occurring in the autoclave may be further accelerated by submitting the ground rbck to a preliminary vacuum. This serves to evacuate air from the autoclave and rock and to draw off the occluded moisture in the rock, and insures the subsequent rapid penetration of the rock byI ithe acid.

This process may be readily carried out in the described apparatus. To do this, rock dust is admitted tov container and' sealed therein. lThe valve 40 isthenopened 'and the vacuum pump'set in operation. It will be^understood that during this time the valve 5 is closed. The autoclave is then rotated while the vaporsin the autoclave are drawn out through the line 20.q To facilitate the removal of the moisture. in therock, steam may be'v circulated throughthe autoclave jacket during a portion of the evacuatingy eriod. .f

After the autoclave has been under a vacuum for the desired period the pump is stopped, -the valve 40 closed and the valve 5 opened. The vacuum within the container, acting as a reverse pressure, draws in the acid with great rapidity and sprays it over the rock. The continuous rotation of the autoclave during this period insures an intimate mixing in the manner described.

After the rock has been treated with the' acid for the desired period, the pressure 1s released in the Amanner described. This quick drop in -,pressure is accompanied by a rapid decrease in temperature which initiates crystallization of the mass. This crystallization can be hastened and the drying of the product'can be accelerated by submitting the mass to a second vacuum. This may be done by opening, the valve 30 and starting the pump of the vacuum motor. The suction set up in the line 20 drains the gases and water vapors from the autoclave. This drop in pressure, occasioned by the vacuum pump, causes a second dro in temperature which aids in completing t e crystallization of the products. l l

The vtime re uire for the com lete process may be ad itionally'shortene bya mitting an extraneous cooling medium to the autoclave jacket during this crystallization and drying period. This may be accomplished by connecting the fluid inlet line, through suitable valve and pipe connections to asource of cooling medium, such for instance as a brine solution. The brine passing through the jacket abstracts heat from the mass in the autocl ve and accentuates the cooling effect of the pressure drop. The quick drop in temperature resulting from hese two causes, assures a rapid and complete crystallization of the product.

After this final treatment in the autoclave, the product comprises a number of relatively small nodules of dry, n'e grained acid phosphate. Tt is removed 'from the autoclave allowing the mass' to deposit in a car or endless belt. It is then transported tothe grinding machine where it is ground to the desire-d size and bagged. L

It will be seen that we have provided an apparatus which is well adapted to carry out the several processes described.v Byusing this apparatus we are enabled to conduct practically the entire treatment of phosphate rock in. a sin le container. As pointed out hereinbefore, t e rock ma Vbe deaerated, intimately mixed with aci converted, crystallized and driedin a single autoclave.- By connecting a vacuum pump to the. autoclave and lproviding the latter with a jacket, we are4 enabled to exercise any desired regulation of the temperature 'and pressure conditions y openingthe lower manhole and' aeaaeae of the process. it is to be noted particnlari" We have eliminated entireiy the conventional apparatus ci the prior art.Y -iir process involves no separate mixing niachinea iarge dens and extensive curing sheds.

The apparatus is carefully devised so as to4 motion transmission line and suitable valves `siii i medium, thereby accelerating crystallization vin the vacuum linej. lt will be seen that the apparatus is susceptible of modification in design and construction of the several parts and hence We do not intend to be restricted l to the particular apparatus shown, since we` conceive the invention to reside broadly in the process set forth and in the mechanical elements adapted to effectuate the process.

We claim :V ,4 l. The method of producing acid -phosphate comprising heating ground phosphate rock in a sealed container While subjecting the container to a vacuum, admitting an acid into the autoclave and rotating the autoclave to insure thorough mixing of the ingredients.,

2. The method of producing acid phosphate comprising mixing ground phosphate rock and an. acid inv a sealed container, rotating vsaid container retaining the autogenous pressure and temperature, of chemical reac tion, applying extraneous heat during reaction, suddenly reducing pressure to normal atmospheric value, and then subjecting the product to a vacuum. j t

3. The method of producing aci-d phosphate comprising mixing ground phosphate rock and an acid in a sealed rotating container, retaining the autogenous pressure and temperature of chemicai reaction, applying extraneous heat during reaction,` suddenly reducing pressure to normal' atmospheric value, then subjecting the product to a vacuum and reducing its temperature with a cooling medium, thereby accelerating crystallization and drying. l I

4. The method of producing acid phos phate comprising mixing ground phosphate rock and an acid in a'sealed rotating container, retaining the autogeiious pressure and temperature of chemical reaction, applying extraneous heat during reaction, suddenly reducing pressure to normal atmospheric value, then subjecting the product to a vacuum and reducing its temperature with a cooling and immediately grinding to desired size.

in testimon tures.

EDWARD HYATT WIGHT.

BEVERLY OBER.

i7 and drying9 and removing container y whereof We afiix our signa- 

